what welder for floorpans?

If you try to weld sheetmetal with a stick, you will drive yourself crazy filling holes. The best you can hope for is to build the buggers up thick enough to weld to, then grind it into the shape of your part. I welded my mufflers to the exhaust pipes and turn-outs with a bunch of 6010s on the lowest setting and the best thing to come out of that little experiment was a sunburn and the knowlege that I can slither my fat butt out from under a pick-up truck in under 3 seconds to get a fire extinguisher! You'll be much happier with a mig (point and shoot)!